We all have a tendency to judge whether decisions were right or wrong decisions by their outcome.

Yet, decision scientists have always cautioned against such an approach. They stress that outcomes are always to some degree unpredictable and that decisions should be judged according to whether they were the right decisions given the information that was available at the time the decision was made.

It is therefore worth reflecting on three decisions that have played a crucial role in the Brexit process: David Cameron’s decision to include an EU referendum in the 2015 Conservative Party manifesto, Theresa May’s decision to call a 2017 election and the ERG’s decision to challenge Mrs May’s leadership in December.

David Cameron’s decision was, reportedly, taken on the basis of two beliefs. One that the Tories would not win an absolute majority and that the Lib Dems would block a referendum in any coalition agreement. The second that, if a referendum were to be held, remain would win in any case.

Neither of these assumptions had any kind of factual support. The outcome of the 2015 election was always going to be unpredictable. And serious polling around the potential outcome of a referendum did not start until after the election. At the time the decision was made, there was no way of knowing how a referendum would eventually turn out.

Cameron’s decision was therefore a blind decision based on assumptions about the unknowable. Bad decision. And it would still have been a bad decision had the referendum result turned out differently.

When May called the 2017 elections, she had a wafer thin majority which she knew would likely be insufficient to push through anything on Brexit since everything was likely to be contentious. The Conservative Party had a 20 point lead in the polls and Mrs May’s personal ratings far outstripped those of Jeremy Corbyn’s.

What sunk the election was a disastrous Tory election campaign and Mrs May’s personal inability to campaign and effectively connect with the voters. Neither of these was knowable, or even reasonably predictable, at the time of the election.

At the time the decision was made, it was therefore a perfectly reasonable way to go. Good decision. And the fact that it was a good decision is not altered by its bad outcome.

As for the ERG, they clearly did not do enough homework to work out whether their challenge to Mrs May’s leadership had a good chance of success. Collecting such information is notoriously difficult because MPs are known to lie furiously about their voting intentions. But this limitation is well known and can be taken into account in calculating one’s chances of success.

The ERG decision was clearly driven by frustration and the group’s desired Brexit outcome. It was not based on a serious and comprehensive collection of evidence. Bad decision.

It was a bad decision on other levels also. Removing Mrs May was never going to be a sufficient achievement for the ERG. They would need to replace her with one of their own. Another highly unpredictable process. And if their coup failed, Mrs May would be protected from formal challenge for another 12 months – as is now the case.

Overall a very bad decision on the information that was available at the time and the relative risks attached to success and failure.

If one buys into all this logic, then Mrs May’s 2017 election decision was the only right decision made of the ones analysed.

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